I would trim all 4 sections into the same size, so that you would have a 35" square. Remember that you will have your seam allowance so your finished size will be 1/2" smaller than cut. Rectangles don't work quite the same way as squares and right angles.
What ever the measurement is, go to this site and plug it in:
https://www.quiltersparadiseesc.com/...Calculator.php
That should give you more help as well
Edit if in time -- for the most stable cut for the corner/setting triangles you would want to start with a square and cut down the diagonal, That will give you the straight grain on the outer edges.